1. Field of the Invention
This invention relates to a process for producing alkylene glycol esters, e.g., ethylene glycol esters, and more particularly, to the oxidative acylation of olefins.
2. Description of the Prior Art
Alkylene glycol esters are useful as solvents and plasticizers. For example, ethylene glycol esters may be used as a solvent, or as an intermediate in the manufacture of ethylene glycol which is a commercially significant intermediate to polyethylene terephthalate.
A variety of catalysts are known to be useful for the production of alkylene glycol esters by the reaction of olefins, carboxylic acids and molecular oxygen.
U.S. Pat. No. 3,770,813 to Kollar, issued Nov. 6, 1973 discloses a process employing a catalyst system consisting of iodine (or an iodine producing compound and oxygen) and at least one cation selected from the group consisting of alkali metal cations, a heavy metal cation of atomic number 21-30 and 48, and nitrogen-containing cations derived from tri-lower alkyl amines, ammonia, piperidine or pyridine. The drawback of this process is relatively low reaction rates which require the use of high reaction temperatures in the range of 130.degree. to 160.degree. C, and relatively higher reaction pressures.
U.S. Pat. No. 3,689,535 to Kollar, issued Sept. 5, 1972, discloses a process which involves the use of a catalyst system consisting of bromine or chlorine (or a bromine or chlorine containing compound) and a variable valence metal cation such as Ce, Mn, Sb, V, Ga, As, Cr, Cu, Ag and Co. This process suffers from relatively low reaction rates which require the use of high reaction temperatures in the range of 80.degree. to 200.degree. C. A further disadvantage of this process is the corrosion problem associated with the corrosive nature of this catalyst system at high temperatures.
U.S. Pat. No. 2,519,754 to Gresham et al, issued Aug. 22, 1950, discloses the use of hydrogen halides (preferably hydrobromic acid) or organic halides (preferably aliphatic bromides) as a catalyst. However, this process requires the use of high reaction temperatures in the range of 180.degree. C to 220.degree. C.
U.S. Pat. No. 3,427,348 to Olson, issued Feb. 11, 1969 discloses a catalyst system consisting of selenium dioxide and a mineral acid. The disadvantage of this catalyst system is relatively low selectivity.
U.S. Pat. No. 3,778,468 to Kollar, issued Dec. 11, 1973, discloses a process for the production of ethylene glycol esters employing a catalyst comprising cationic selenium and at least one halogenated substance selected from the group consisting of elemental bromine, elemental chlorine, a bromide-producing compound and a chloride-producing compound.
U.S. Pat. No. 3,668,239 to Kollar, issued June 6, 1972, discloses a catalyst system consisting of tellurium and an appropriate bromine source.
U.S. Pat. No. 3,479,395 to Huguet, issued Nov. 18, 1969, discloses a catalyst system consisting of tellurium dioxide, an alkali metal halide and a redox system.
U.S. Pat. No. 2,497,408 to Gresham, issued Feb. 14, 1950, discloses a process for the manufacture of propylene glycol esters employing a mixed catalyst of a metal acetate such as lead acetate or ferric acetate and an alkaline earth metal acetate.
U.S. Pat. No. 3,299,110 to Pine, issued Jan. 17, 1967, discloses a molybdenum-containing catalyst such as molybdenum sulfide, molybdenum oxide and sulfided cobalt molybdate.
British Pat. No. 1,058,995 discloses a catalyst system consisting of palladium II salt, metal acetate such as alkali metal, alkaline earth metal, cupric, ferric, stannic and nickel acetates, and a metal halide selected from alkali metal, alkaline earth metal, cupric, ferric, stannic and nickel chlorides and bromides.
British Pat. No. 1,124,862 discloses a catalyst system consisting of a palladous salt and a nitrogen oxide such as a nitrate or nitrite of a metal of Group I, II or VIII of the Periodic Table, nitric acid, nitrous acid, NO, NO.sub.2, N.sub.2 O.sub.5 or N.sub.2 O.sub.3.
U.S. Pat. No. 3,262,969 to Clark et al, issued July 26, 1966, discloses a catalyst system consisting of a palladous salt, a salt of a carboxylic acid, an alkali metal halide and a redox system.
U.S. Pat. No. 3,349,118 to Kohll et al., issued Oct. 24, 1967, discloses a catalyst system consisting of palladium halides (preferably chloride) and nitric acid.
U.S. Pat. No. 3,859,336 to Aguilo et al., issued Jan. 7, 1975, discloses a catalyst system consisting of noble metal halides and nitrogen oxides such as nitric acid, nitric oxide and nitrogen dioxide. It also discloses that the halogens of the noble metal halides are preferred in order of decreasing atomic weight.
However, the processes employing a noble metal salt as a main catalyst pose the disadvantages such as a loss of the expensive noble metal salt during the operation, plugging of the system caused by the deposit of the noble metal, and relatively low selectivity caused by the formation of unwanted by-products such as aldehydes and ketones. There is a need, therefore, for a more efficient, selective and inexpensive process for the production of alkylene glycol esters from olefins and carboxylic acids.